GOODWILL AND INTANGIBLE ASSETS - Amortized Intangible Assets - (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 01, 2017	Mar. 26, 2016	Mar. 28, 2015	Dec. 31, 2016
Components of amortized intangible assets
Gross Carrying Amount	$ 206,648			$ 205,079
Accumulated Amortization	126,160			121,486
Amortization expense for intangible assets	3,863	$ 3,995
Estimated amortization expense
2015	15,243
2016	13,560
2017	12,819
2018	11,749
2019	9,690
Customer Relationships
Components of amortized intangible assets
Gross Carrying Amount	192,743			191,316
Accumulated Amortization	$ 115,792			111,342
Weighted Average Life	13 years		13 years
Proprietary Software & Database
Components of amortized intangible assets
Gross Carrying Amount	$ 3,671			3,616
Accumulated Amortization	$ 3,089			3,056
Weighted Average Life	8 years		8 years
Patents & Proprietary Technology
Components of amortized intangible assets
Gross Carrying Amount	$ 6,485			6,434
Accumulated Amortization	$ 3,566			3,420
Weighted Average Life	11 years		11 years
Other
Components of amortized intangible assets
Gross Carrying Amount	$ 3,749			3,713
Accumulated Amortization	$ 3,713			$ 3,668
Weighted Average Life	3 years		3 years